Such a system is disclosed in U.S. Pat. No. 4,881,227. Here, a two-processor system for a motor vehicle is described wherein the two processors carry out control functions in the motor vehicle while mutually exchanging data. An operational cycle of the motor vehicle is initiated generally by closing the ignition switch. At the beginning of an operating cycle, the two processors carry out a so-called cold start which is triggered by a so-called "power-on-reset" pulse. In addition, measures are suggested which detect an error condition in the computer system with the aid of the cyclical data exchange between the two processors and by means of further mutual monitoring devices such as watch dogs. Furthermore, the possibility is provided for each processor to start or reset the other processor after that processor has detected an error condition in the computer system.
As a rule, and especially for applications with respect to safety-relevant control systems in motor vehicles, the measures for cold starting the computer system include extensive tests and checks of different components which are absolutely necessary for carrying out the control functions. Measures of this kind occupy the computer system because of their extent for a certain time during which the computer system is inactive with reference to the control functions. It is therefore not desirable that these measures following a cold start be carried out for each reset of a processor because of an error condition or because of cyclical restarts undertaken possibly during operation. The known computer system offers no possibility of distinguishing between warm and cold starts of the system so that with each reset the same extensive sequence of steps is run through. However, this limits the availability of the computer system. The desire to distinguish the operable processor from the inoperable processor in a two-processor system is attempted to be satisfied in the above-mentioned system by means of extensive checks and monitoring which likewise tie up the processors for some time.